Pumps and valves for transporting and manipulating liquids in microfluidic devices are essential for developing lab on a chip technology. Various approaches to designing micro-fluidic pumps and valves have been attempted. However, each of these conventional approaches suffers from its own limitations.
The two most common methods of producing microelectromechanical (MEMS) structures such as pumps and valves are silicon-based bulk micro-machining (which is a subtractive fabrication method whereby single crystal silicon is lithographically patterned and then etched to form three-dimensional structures), and surface micro-machining (which is an additive method where layers of semiconductor-type materials such as polysilicon, silicon nitride, silicon dioxide, and various metals are sequentially added and patterned to make three-dimensional structures).
A limitation of the first approach of silicon-based micro-machining is that the stiffness of the semiconductor materials used may necessitate high actuation forces, which in turn result in large and complex designs. In fact, both bulk and surface micro-machining methods are limited by the stiffness of the materials used. In addition, adhesion between various layers of the fabricated device is also a problem. For example, in bulk micro-machining, wafer bonding techniques must be employed to create multilayer structures. On the other hand, when surface micro-machining, thermal stresses between the various layers of the device limits the total device thickness, often to approximately 20 μm. Using either of the above methods, clean room fabrication and careful quality control are required.
Pressure driven valves for devices made out of soft polymers (e.g. PDMS) are described in U.S. Nonprovisional Patent Application No. 09/605,520, incorporated herein by reference for all purposes herein.
From the above, it is seen that utilization of structures and methods for efficient and effective movement of fluids are highly desired.